Effects of the size of cosmological N-Body simulations on physical quantities -- I: Mass Function

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  • 16 January 2006
Abstract
N-Body simulations are a very important tool in the study of formation of large scale structures. Much of the progress in understanding the physics of high redshift universe and comparison with observations would not have been possible without N-Body simulations. Given the importance of this tool, it is essential to understand its limitations as ignoring the limitations can easily lead to interesting but unreliable results. In this paper we study some of the limitations arising out of the finite size of simulation volume. We explicitly construct the correction term arising due to a finite box size and study its generic features for clustering of matter and also on mass functions. We show that the correction to mass function is maximum near the scale of non-linearity, as a corollary we show that the correction term to the multiplicity function and the number density of haloes of a given mass changes sign at this scale; the number of haloes at small masses is over estimated in simulations. The same technique can be used to study corrections on other physical quantities. We point out situations in which a box that is much larger than the scale of non-linearity is used and even then the correction term is comparable to the physical quantity of interest.

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